Cathode ray tube deflecting circuits



Sept. 14, 1937 A. v. BEDFORD 2,092,871

CATHODE RAY TUBE DEFLECTING CIRCUITS Filed July 25, 1935 a m k k *l N :3 "I 2 4- I 4 v q II a =11 N "a M N INVENT'OFI Witness J Aida, 1 Bedford WXM Patented Sept. 14, 1937 lTED STATES PATENT OFFICE 2,092,811- V carnonn nay TUBE DEF'LECTING omom-rs Aida V. word, Collingswood, N; J., asslgnor to Radio Corporation of hmerica, a orporation of'Delaware Application July zsrless serla No. 33.020

5 Claims.

usually does not travel down the exact center of a the tube to strike the center of the fluorescent screen, light-sensitive mosaic, or other surface to be traversed by the beam. Among the reasons in for this are inaccuracies in tube manufacture, the

effect of the earth's magnetic field, and the presence of local;n'uagnetlc fields.

An object of my invention is to provide an improved means for centering the electron beam of iii a cathode ray tube.

' More specifically, an object of my invention is to provide improved centering means in electron beam deflecting circuits which include electrostatic deflecting plat'es.

My invention, preferably, is applied to an electrostatic deflecting circuit for a cathode-ray tube in which the deflecting plates are connected across the secondary winding of a transformer and in which the electrical midpoint of the secondary winding is' maintained at approximately the'same direct current potential as an electrostatic focusing electrode of the cathode ray tube. In one embodiment of my invention provision is made for impressing a direct current potential M upon one deflecting plate through the transform er secondary winding and for impressing a direct current potential upon the other deflecting plate through a resistor 01 comparatively high resistance. Means is provided for simultaneously in- 35 creasing the direct current potential on one deflecting plate and decreasing the direct current potential on the other deflecting plate, whereby the electron b may be properly centered.

m in another embodiment of my invention the deflecting plates are connected has a condenser inserted at its midpoint whereby a direct current ,;potential. may be applied to one deflecting plate through one half of the secondary winding and is to the other deflecting plate through the other half of the said winding.-

Otherobiects, features. and advantages of invention will appear from the following description taken, inconnection with the accompanying drawing, in which v Figure 1 is a circuit diagram of one embodiment of my invention, and

Figure 2 is a circuit diagram of another em- 5 bodiment of my invention.

Ref to Fig. 1, my invention is shown apransformer secondary winding across which the (Cl. 250-27) J plied to a television, transmitter which includes acathode ray transmitting tube l of a well known type. The cathode ray tube I comprises an evacuated enevelope 2 having therein an electron gun comprising an indirectly heated cathode 3, a con- 5 trol electrode 4, and a first anode B. A second anode l is provided which also functions as an electrostatic focusing electrode for focusing the electron beam to a small spot on a light-sens tive mosaic 8.

The mosaic l is so positioned that an image of the object to be transmitted may be formed thereon, and it is also so positioned that it may be scanned by the electron beam to produce pic-' ture signals in an output resistor 9 which is capacitively connected between the mosaic and the second anode l.

The second anode l is connected to ground and the cathode land first anode 6 are maintained at high negative potentials with rmpect to ground by means of any suitable source of potential such as batteries ii and I2. The control electrode 4 is maintained at a negative potential with re- I spect to the cathode 3 by means-of a suitable source of potential suchas a battery I 3.

In order to deflect the electron beam in one plane, electrostatic deflecting plates. l4 and l6 are provided. The deflecting means for deflecting the electron beam in a plane at right angles to the first mentioned plane has been omitted in 80 order to simplify the drawing.

The voltage having a saw-tooth wave shape E which is to be stepped up to a high voltage and applied to the deflecting plates l4 and I8 is impressed upon the input circuit of an output tube I1. The tube il may be a vacuum tube of the three-element type including 9. directly heated cathode l8, a control grid l9, and a plate 2|. The input circuit of the tube I1 includes an input resistor 22 which is connected between the control grid 19 and ground, and a self-biaslng resistor 23 which is connected between ground and the midpoint of apotentiomter 24 connected across the cathode filament H. The self-biasing resister 23 is shunted by the usual by-pass condenser 26.

The plate 2i is supplied with a positive potential from any suitable voltme source (not shown), the voltage being applied to the plate through the primary 2! of a step-down transformer 28. i

' The step-down transformer 28 is employed because the deflecting plates of the cathode-ray tube I are connected to the plate circuit of the output tube ll tin-o a rather long cable, 15 E5 dlcated by the dotted resistor til, the seconda y to 100 feet in length, for example. This ce includes three conductors 2t, 3!, and 32, as incircle. By stepping do the voltage of the saw-tooth wave, more cient transmission is obtained and the loss of high frequency components due to distributed cable capacity is reduced to a small amount.

The secondary 83 of the step-down transformer 28 is connected through the cable conductors 2t and 3!! to the primary of an auto-transformer 34%. The secondary of the auto-transformer is connected to the deflecting plates it and it, the upper end or the secondary being connected to plate id through a condenser 36 and the lower end of the secondary being connected to the plate it through a direct current connection 3?.

The auto-transformer 3- 3 is provided to stepup the voltage of the saw-tooth wave to the necessary high value for producing sumcient deflection of the electron beam.

Referring now to the electron beam centering circuit itself, a variable source of direct current potential is provided for each deflecting plate. One ofthese sources comprises a resistor 38 which is connected in series with another resistor between ground and the positive terminal of the plate supply for the output tube ill. The other source comprises another resistor ll also connected in series with resistor 39 between ground and the positive terminal of the plate supply. Y

The midpoint of the secondary 33 of the stepdown transformer is connected to a variable tap or slider 62 on the resistor 38. It will be seen that there is a direct current connection from the second anode B through ground, through the t3, the cable conduc tors 29 and thand the auto-transformer 3 3 to the deflecting plate 06. Therefore, by moving the slider t2, the direct current potential of the deflecting plate ill with respect to the second anode or focusing electrode l may be adjusted.

A direct current connection is also provided between the deflecting plate id and the second anode i. This connection includes a resistor 68 of comparatively high resistance value which connects the deflecting plate it to an adjustable tap or slider 5 3 on the resistor iii. It will be apparent that by lusting the slider dd the direct current potential of the deflecting plate id may be varied with respect to the focusing electrode 71. Preferably, the two resistors 8t and iii are so connected with respectto each other that adjacent ends are of opposite polarity. The sliders 32 and it may be mechanicall connected as indicated by the dotted block '6, whereby a move== ment of one slider in a direction toe one defleeting plate more positive with respect to ground simultaneously causes a movement of the other slider to make the other deflecting plate less positive witnrespect to ground.- Thus, by adjusting the sliders t2 and it, the electron may be centered on the mosaic e.

conductors are required. In Figs.

Aid is inserted at the midpoint of the -w -r Since the resistor ill loads the upper or the auto-transformer secondary, it may be desirable in some cases to load the other half by means of a resistor (ll of approximately the e value. In general, however, it has been found that this additional loading of the secondary is not necessary for good operation.

Inthe circuit shown in Fig. 2, only two cable 1 and 2 like parts are indicated by the same reference numerals. In the circuit shown in 2, a comic tap M on to said focusin aooasvi of the step-down transformer 28, and another condenser fit is inserted at the midpoint of the winding of the auto-transformer 3 3. Direct current potential is applied to the deflecting plate is by means of a connection from the variable the resistor M to one half of the secondary 33 of the step-down'transformer 28. A direct potential is applied to the deflecting plate it by means of a connection from the variable tap 32 on the resistor lg .to the other half of the secondary 33 of the transformer 28. In this way a direct current potential is applied to each deflecting plate through a cable conductor and through one section of the auto-transformer 3d. The electron beam may be centered, as described above, by adjusting the variable taps on the resistors lit and ii.

In order to obtain the best electrostatic focusing of the electron beam the deflecting plates i l and it should be at the same direct current potential as the focusing electrode i. For the purpose of centering the electron beam this ideal condition is departed from to a certain extent, but the total voltage drop across each of the resistors 36 and M is small, about 50 volts, as compared with the voltage diflerence betwen the cathode 3 and focusing electrode 6.

It has been found that when the deflecting plates are not maintained at the same direct current potential as the focusing electrode, the focusing of the electron beam is improved if one deflecting plate is maintained above the focusin electrode potential by the same amount that the other deflecting plate is maintained below the focusing electrode potential. This adjustment may be made by means of a source of potential such as a battery 5i which may be adjusted to give the electrode 8 the proper potential with respect to ground.

It should be understood that my invention is not limited to the particular type of cathode-ray tube illustrated. it may be applied equally well to other types of cathode-=ray tubes, such as those having fluorescent screens therein forthe reproduction of a picture at a television receiver.

The values of certain elements have been indicated on the drawing in ohms, megohms and micrcfarads. lit should be understood that these values are given merely by way of example and may be varied within wide limits.

From the foregoing description it will be appar-= out that various other mocations may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be imposed thereon as are necessitated by the prior art and set forth in the appended cla.

I claim as my invention:

1. In combination, a cathme ray tube having therein an electron gun for producing an electron Ziflll means including a focusing electrode for electrostatically focusifig said beam, a pair of deflecting plates for deflecting said beam, said plates being on opposite sides of said cathode ray, and means for simultaneously adjusting the direct current potentials of said plates with respect electrode.

2. In combination, a cathode ray tube having therein means including a plurality .of electrodes for producing an electron beam, a pair of deflecting plates for deflecting said beam, said plates being on opposite sides of said beam means for applying a periodic deflecting voltage across said plates, and means for simultaneously so adjusting the ct current potentials of said plat beam may be centered from a position oneither with respect to one of said electrodes that said side of center.

3. In combination, a cathode-ray tube having therein means including a plurality oi electrodes for producin an electronbeam, a pair of'deflecting plates to deflecting said beam, means for applying a periodic deflecting voltage across said plates, and means for giving one of said deflecting plates a more positive direct current potential with respect to one of said electrodes and for simultaneously giving the other of said deflecting plates a niorenegative direct current potential with respect to said one electrode.

4. In combination, a cathode-ray tube having a pair of deflecting plates and an electrostatic focusing electrode, an auto-transformer having one end of its secondary coupled to one of said plates through a direct-current connection and having the other end of its secondary connected to the other of said lates through a condenser, a pair oficonductors, means for applying a periodic deflecting voltage across the primary or said transformer throughsaid conductors, adjustable means for applying a direct current potential to one of said plates through said conductors whereby its direct current potential with respect to.

said focusing electrode may be varied, a resistor having one end connected to the other or said plates through a direct current connection, and

- adJustable means for so applying a direct current potential to said other plate through said resistor that its direct current potential with respect to said focusing electrode may be varied.

5. In combination, a cathode-ray tube having a pair of deflecting plates and an electrostatic focusing electrode, an auto-transformer having a primary and a secondary, a condenser connected in series with and between two sections of said primary, one of said plates being connected to one end of said secondary through a direct current connection, the other of said plates being connected to the other end oi said secondary through another direct current connection, a pair 01' conductors, means for applying a periodic deflecting potential across said primary through said conductors, and adjustable means for applying direct current potentials to said plates through said conductors whereby their direct current potentials with respect to said focusing electrodes may be varied for centering the cath-' ode ray.

ALDA V. BEDFORD. I 

